Home  www.playhookey.com  Fri, 07252014 

Direct Current

Alternating Current

Semiconductors

Digital

Logic Families

Digital Experiments

Computers

 Analog  Analog Experiments  Oscillators  Optics  HTML Test  

 The Basics  Variations in Feedback Circuits  Mixing Analog and Digital Technologies  Generating Waveforms  Operational Amplifiers   
 A Square Wave Generator  A Triangle Wave Generator  A Sine Wave Generator  
Generating Triangle Waves 

In the basic square wave generator circuit, a graduallycharging capacitor was used to help set the timing or frequency of the circuit. However, since it was only charging through a resistor, it necessarily charged on a logarithmic curve, rather than as a linear ramp. Can we use an op amp integrator here to obtain a linear triangle wave along with the square wave?
In the circuit to the right, we use a separate integrator to generate a ramp voltage from the generated square wave. As a result, we can get both waveforms from a single circuit. The phase relationship shown between the two output waveforms is correct — remember that the integrator inverts as well as integrating, so it will produce a negativegoing ramp for a positive input voltage, and viceversa.
Because we are now using an op amp integrator to get the triangle wave, we no longer have a logarithmic response anywhere in the circuit. Therefore, the equation for the operating frequency is simplified to:
f_{out} =  1  (  R_{2}  ) 
4R_{t}C  R_{1} 
The squarewave amplitude is still the limit of voltage transistion, which we are assuming here to be ±10 volts. The triangle wave's amplitude is set by the ratio of R_{1}/R_{2}. Note that for this circuit to function, it is necessary that R_{1} be less than R_{2}. This keeps the triangle amplitude less than the square wave amplitude. It is also necessary for the resistor values to be within a reasonable range for correct operation of the op amps. There is no restriction on the value of C.


 
All pages on www.playhookey.com copyright © 1996, 20002013 by
Ken Bigelow Please address queries and suggestions to: webmaster@playhookey.com 